Short-term effect of changing water regimes on the soil nematode community in rice-duckweed system under water-saving irrigation

Abstract

Rice agroecosystems have garnered global attention owing to a unique transition from traditional flooding to water-saving practices, such as alternate wetting and drying (AWD) irrigation, which features a dual-habitat ecosystem with high biodiversity throughout the growing period. Nematodes' taxonomic bioindication potential could reveal perturbations in the soil environment and changes in food web status under AWD. However, the influence of changing dual modes (dry and wet habitats) with duckweed (D) on nematodes was often overlooked. Therefore, a field experiment was conducted to quantify the impact of flooding irrigation, and alternate wetting and drying irrigation on nematode abundance across four treatments: flooding irrigation with (FI + D) and without duckweed (FI), alternate wetting and drying irrigation with (AWD + D) and without (AWD) duckweed. For flooding irrigation, soil samples were taken at tillering, pre-mid-season drainage (MD), and at flowering post-MD. Similarly, for alternate wetting and drying irrigation at tillering and flowering for respective dry and wet cycles. The first AWD dry-cycle with duckweed (AWD + D) significantly reduced nematode abundance compared to the wet cycle (AWD + D) (P < 0.033). In FI, MD significantly reduced nematode abundance (P < 0.007) compared to FI + D. Factor prediction analytics showed that pH in the FI post-MD and $\left[{\text{NH}}_4^{+}-N\right]$ in flooded and AWD-integrated treatments were the most influential abiotic drivers governing nematode taxonomic and functional diversity. AWD dry-wet cycles with duckweed, fuel colonizer CP (1–2, r-strategists) nematodes, indicating better soil health and higher microbial turnover than without duckweed. The AWD drying cycle with duckweed produced more mature, fertile soils with balanced bacterivores/fungivores and moderate C:N ratios, and demonstrated suppressive properties, which further seek an investigation into the link between soil biochemical enrichment from decomposing duckweed.